Polymeric composites that contain organic and/or inorganic filler materials have become desirable for a variety of uses because of their excellent mechanical properties and weathering stability. Foamed versions of these materials can have a relatively low density yet the filler materials can provide a composite material that is extremely strong. The polymer provided in the composite can help provide good toughness (i.e., resistance to brittle fracture) and resistance to degradation from weathering to the composite when it is exposed to the environment. Thus, polymeric composites including organic and/or inorganic fillers can be used in a variety of applications, including in building materials.
The use of polyurethane composites has grown over the last three decades. This can be attributed to their superior tensile strength, impact resistance, and abrasion resistance compared to, for example, unsaturated polyester and vinyl esters based composites. However, a persistent problem in making polyurethane composites is the exotherm within the polyurethane composite mixture which results from the reaction between the isocyanate and the hydroxyl groups in the reaction mixture. Excessive heat results in scorching or surface blemishes on the surface of molded product. In continuous molding processes, increasing the reactivity of the system such as by increasing catalyst has been used to reduce demolding times; however, the increased reactivity results in increased heat generation and thus an increase in surface blemishes.